Replaced my 2 House/ Auxiliary batteries with 2 Crown True Deep Cycle 12v batteries. Group 27, 115 amp hours each. If I had the Height in my battery box, I'd be using 6 volt golf cart batteries in series, as they are even burlier deep cycle batteries.
Not Cheap at 105$ each before tax, but they are true deep cycle 12 volt batteries.http://www.solar-electric.com/repoba12vo11.html
Most batteries which say deep cycle/rv/marine are dual purpose batteries. Wally world everstarts dual purpose batts could be had for 82$ per battery in my area. Better than a starting battery for deep cycle use but 8 to 12 pounds lighter than the Deep Cycle Crowns of equal size.
My engine starting battery is almost 5 years old now and is just about done too. But the New Deep cycles together have about twice the required CCA to start my engine.